This invention is directed to gasifiers for processing carbonaceous fuels and more particularly to a novel protective refractory shield that is mechanically secured against a protectable surface of the gasifier.
The processing of carbonaceous fuels, including coal, oil and gas to produce gaseous mixtures of hydrogen and carbon monoxide, such as coal gas, synthesis gas, reducing gas or fuel gas is generally carried out in a high temperature environment of a partial oxidation gasifier with operating temperatures of approximately 2400.degree. F. to 3000.degree. F. Partial oxidation gasifiers, an example of which is shown in U.S. Pat. No. 2,809,104, are operable with an annulus type fuel injector nozzle for introducing pumpable slurries of carbonaceous fuel feed components into a reaction chamber of the gasifer along with oxygen containing gases for partial oxidation. The annulus type fuel injector nozzle, which is a well known structure, is generally formed of metal such as super alloy steel, to enable it to withstand the relatively high operating temperatures of the gasifier.
The coal-water sluny that passes through an outlet orifice of the fuel injector nozzle normally self-ignites at the operating temperatures of the gasifier. Self-ignition of the fuel feed components usually occurs at a region close to the outlet orifice of the fuel injector nozzle, also known as the reaction zone. The reaction zone is generally the highest thermal gradient zone in the gasifier and the temperature conditions at the reaction zone can cause thermal induced fatigue cracking at the outlet orifice of the fuel injector nozzle.
During gasifier processing of the coal-water slurry component that is fed through the fuel injector nozzle, one of the reaction products is gaseous hydrogen sulfide, a well known corrosive agent. Liquid slag is also formed during the gasification process as a by-product of the reaction between the coal-water slurry and the oxygen containing gas, and is another well known corrosive agent.
Because the outlet orifice of the fuel injector nozzle is exposed to corrosive gases and corrosive slag while operating at the extreme temperature conditions previously described, it is particularly vulnerable to breakdown caused by heat corrosion, thermal induced fatigue cracking and chemical deterioration, also referred to as thermal damage and thermal chemical degradation. Once there is a breakdown of the fuel injector nozzle shut down of a gasifier is unavoidable because the gasification process cannot be carried out until repair or replacement of the fuel injector nozzle is accomplished.
Any shutdown of an operating gasifier is costly because of the termination of synthesis gas ("syngas") production which is normally continuous when the gasifier is in operation. The downtime that is usually required before a fuel injector nozzle can be repaired or replaced can be approximately 8 hours if there is no damage to the refractory of the gasifier. In a typical gasifier 8 hours downtime translates into a significant loss of syngas production. If there is damage to the refractory of the gasifier a substantially longer downtime than 8 hours is usually required for repair of the gasifier.
Since the fuel injector nozzle is one of the most vulnerable components in the gasifier and operational shutdowns attributable to fuel injector nozzle repair and placement generally result in substantial losses of syngas production there have been going efforts to extend the operating life of the fuel injector nozzle.
Attempts to extend the operating life of a fuel injector nozzle especially by fording some means of high temperature and corrosion protection to the outlet orifice area are well known. For example U.S. Pat. No. 4,491,456 to Schlinger shows a thermal shield for a fuel injector nozzle. The thermal shield is held in vertical orientation around the fuel injector nozzle by a bonding material that joins the thermal shield to a protectable surface of the fuel injector nozzle. However, the bonding material is subject to substantially the same temperature conditions as an unprotected fuel injector nozzle and is thus vulnerable to thermal damage and consequential thermal chemical degradation which can cause failure of the bonding material. Failure of the bonding material will permit the thermal shield to fall away from the outlet end of the fuel injector nozzle, thereby directly exposing the outlet end to the corrosive and thermally damaging ambient conditions in the gasifier.
Published Canadian application 2,084,035 to Gerhardus et al shows protective ceramic platelets to clad the surface of a fuel injector nozzle. The ceramic platelets are held in place by a dovetail projection formed on the platelet that engages a complementary shaped dovetail slot formed in the end surface of the fuel injector nozzle. The dovetail slot formations in the end surface of the fuel injector nozzle are sections of reduced thickness with inside corners that are stress concentration areas vulnerable to cracking and thermal damage. In addition, the dovetail projection on the ceramic platelets have a narrow support neck that is likely to be an area of weakness or breakage. Breakage of the support neck can cause the ceramic platelets to fall away from the end surface of the fuel injector nozzle.
It is thus desirable to provide a protective refractory shield for a protectable surface inside the gasifier, including the outlet orifice of a fuel injector nozzle, wherein the protective refractory shield can be mechanically secured to the protectable surface without the need to recess the securement structure or the refractory material in the protectable surface.
During the gasification process molten slag gradually flows downwardly along the inside walls of the gasifier to a water bath of the type shown in U.S. Pat. No. 5,464,592. The molten slag, before reaching the water bath, flows through a throat section at a floor portion of the gasifier and closely past a quench ring and dip tube that leads to the water bath. The quench ring, which is formed of a chrome nickel iron alloy or nickel based alloy such as Incoloy is arranged to spray or inject water as a coolant against the walls of the dip tube. However the quench ring, which includes downwardly directed surfaces that can be contacted by molten slag, may experience temperatures of approximately 1800.degree. F. to 2800.degree. F.
Because the quench ring can be exposed to the molten slag and corrosive gases at temperatures of approximately 1800.degree. F. to 2800.degree. F. it is vulnerable to thermal damage and thermal chemical degradation, especially at the downwardly directed surfaces that surround the dip tube. If the downwardly directed surfaces of a quench ring are thermal shielded with a bonded refractory material, high temperature degradation of the bonding material is likely to occur resulting in fall off of the refractory material from the protectable surface.
It is thus desirable to provide a quench ring with a protective refractory shield that does not require bonding of the refractory material to a protectable surface and does not require recessing of the refractory material in the protectable surface.